There are many species of coffees having different aromas and tastes (e.g., sweetness, mellowness, bitterness, body and acidity) and they range from low-grades represented by low-priced robustas to high-grades represented by high-priced arabicas. People select and drink one or more kinds of coffee according to their preference.
There are also many species of other drinks such as tea, ptisan and oolong tea and people drink one or more kinds of these drinks according to their preference.
In general, soft drinks which are prepared from coffee beans and various kinds of tea leaves are usually manufactured by extraction from raw materials, dilution, dissolution, blending and packaging, followed by heat sterilization at 100.degree. C. or higher for maintaining a commercially acceptable aseptic condition.
Although the pH of soft drinks is generally not lower than 4.6, their ingredients will undergo pH drop during heat sterilization. As a result, the soft drinks have an undesirable acid taste and incur significant deterioration of aroma and taste in the course of time. Hence, it is essential to adjust the pH of soft drinks.
Particularly in the case of drinks containing a dairy product such as coffee and tea with milk, otherwise stably dispersed lactoproteins are aggregated at a pH below 6 to produce a precipitate. To prevent this problem, it is necessary to adjust the pH of those drinks.
For the purpose of preventing the undesirable acid taste, deterioration of aroma and taste with time or precipitation of a dairy product, the pH adjustment of soft drinks has been conducted using sodium bicarbonate (sodium hydrogencarbonate), disodium hydrogenphosphate or the like.
However, the use of sodium salts such as sodium bicarbonate, disodium hydrogenphosphate and the like for pH adjustment causes saltiness, sliminess and a bad aftertaste in drinks, which result in the deterioration of their characteristic aromas and tastes. It is believed that such deterioration in the aroma and taste of drinks is caused by the change in the aroma and taste balance due to the increase in the sodium ion concentration which occurs after addition of an excess amount of sodium salts to drinks which are prepared from coffee beans and various tea leaves that contain only a very small amount of the sodium ingredient.
Therefore, there is strongly desired the development of pH adjustors which can adjust drinks to a desired pH without deteriorating their aroma and taste. The development of such pH adjustors has very great industrial significance.